Embodiments of the inventive concept relate to semiconductor memory devices, and more particularly, to flash memory devices and data storage devices incorporating same.
Semiconductor memories are important microelectronic components in digital logic systems, such as computers and microprocessor-based applications ranging from satellites to consumer electronics. Advances in the fabrication of semiconductor memories including process enhancements and technology developments enable scaling that provides greater integration density and faster operating speeds. Improvements in semiconductor memories further enable performance of incorporating digital logic systems.
Semiconductor memory devices may be classified according to their operative nature as being either volatile or non-volatile. Volatile memory devices enjoy relatively fast operating characteristics, but lose stored data in the absence of applied power. Volatile memory devices include random access memories (RAMs) that store data either by setting up the logic state of a bi-stable flip-flop, as in a static random access memory (SRAM), or by charging a capacitor, as in a dynamic random access memory (DRAM).
Non-volatile memories do lose stored data in the absence of applied power, and include, as examples, Mask Read-Only Memory (MROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), and Electrically Erasable Programmable Read-Only Memory (EEPROM). Data storage for a non-volatile memory may be a one-time use or reprogrammable use depending on the technology used to fabricate the memory device. Non-volatile memories are used to store microcode in a wide variety of applications in the computer, avionics, telecommunications, and consumer electronics industries. A combination of single-chip volatile as well as non-volatile memory storage modes is also available in devices such as non-volatile SRAM (nvSRAM) for use in systems that require fast, programmable non-volatile memory. In addition, dozens of special memory architectures have evolved which contain additional logic circuitry that optimizes performance for specific application tasks.
Within the broader class of non-volatile memories, the MROM, PROM, and EPROM are not capable of being freely erased and written to using normally available system resources. Thus, they are not practically suitable for use in many applications. In contrast, the EEPROM is capable of being electrically erased or written. Hence, the EEPROM has been widely adopted for use within many different applications including auxiliary memories, frequently updated memory components, etc. Flash memory is a common form of the EEPROM and includes NAND type and NOR type flash memory.